[R] error using boxcox.nls during non linear estimation

[Francisco Mora Ardila]

Hi all

I´ve got a problem using boxcox.nls function in nlrwr packagge. I´m fitting several non 
linear models to these data:

> x
 [1]   2   1   1   5   4   6  13  11  13 101 101 101

> y
 [1]  1.281055090  1.563609934  0.001570796  2.291579783  0.841891853
 [6]  6.553951324 14.243274230 14.519899320 15.066473610 21.728809880
[11] 18.553054450 23.722637370

I used nls function with self starters, for example SSgompertz:

model<-nls(y~SSgompertz(x,a,b))

The model runs OK, with the following summary:

Formula: y ~ SSgompertz(x, a, b, c)

Parameters:
  Estimate Std. Error t value Pr(>|t|)    
a  21.2426     0.9689  21.924 4.03e-09 ***
b   5.3330     1.4722   3.622  0.00555 ** 
c   0.8045     0.0274  29.364 3.01e-10 ***
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 

Residual standard error: 1.686 on 9 degrees of freedom

Number of iterations to convergence: 5 
Achieved convergence tolerance: 1.508e-06 

But then, trying to use boxcox.nls(model) gives the following error:

> boxcox.nls(model)

Error in eval(object$data)[, as.character(formula(object)[[2]])[2]] : 
  object type 'environment' is not a subset

(this last part traduced from spanish)

I´ve tryed other functions, even without self starters but it does not work. Then it 
seems to be there something in the data, but I don´t know what.

Any suggestions?

Francisco


----------------------
Francisco Mora Ardila
Estudiante de Doctorado
Centro de Investigaciones en Ecosistemas
Universidad Nacional Autónoma de México